Preparation of para-dialkyl substituted aromatic compounds



Fat-elated June 10, 1958 PREPARATION OF PARA-DIALKYL SUBSTITUTED AROMATIC COMPOUNDS Herman S. Bloch, Chicago, 111., assignor to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware No Drawing. Application March 8, 1955 Serial No. 493,060

6 Claims. (Cl. 260-668) I This invention relates to a process for preparing paradialkyl'substituted aromatic compounds, and more particularly to a process for preparing para-xylene.

The increased use of terephthalic acid as an inter mediate in the preparation of synthetic fibers of the glycol-terephthalic type has increased the demand for para-xylene from which the terephthalic acid is prepared. Heretofore, the separation of pa ra-xylene from its orthoand meta-isomers has been relatively expensive due to difiiculties encountered in the process involving the separation of the aforementioned isomers. For example, one method for preparing para-xylene from ethylbenzene and isomers of said para-xylene is to subject the mixture xylene, m-xylene, p-xylene and ethylbenzene) to fractional distillation. However, inasmuch as para-xylene, meta-xylene and and ethylbenzene all boil within a 3 C. range of each other, separation into the various compo nents by fractional distillation is relatively difiicult to accomplish.

One method of operation is to distill out the o-xylene which has a boiling point of approximately 5 to 6 above that of the other three components of the mix ture. The paraand meta-xylene along with the ethylbenzene will then be separated into several fractions, and para-xylene is then separated out by crystallization from cuts containing the highest percentage. Another method of separating the para-xylene from the unwanted isomers is to displace the eutectic compositions of paraand meta-xylenes by the addition of a co-crystallizing agent such as carbon tetrachloride followed by cooling, the para-xylene and carbon tetrachloride thereby separating out of the mixture, and thereafter recovering said para-xylene by fractional distillation of the para-xylenecarbon tetrachloride mixture.

Still another method of recovering para-xylene is to partially sulfonate the mixture, separate the unsulfonated layer from the reaction mixture and crystallize the paraxylene from the mixture by lowering the temperature.

7 It can readily be seen from the above description that obtaining relatively pure para-xylene for the manufacture of terephthalic acid involves many steps which, as hereinbefore set forth, are relatively difficult and expensive to accomplish.

It is therefore an object of this invention to provide a relatively inexpensive and novel process for obtaining para-dialkyl substituted aromatic compounds.

A further object of this invention is to provide a process for preparing para-dialkyl substituted aromatic compounds such as para-xylene by condensing specific ketones and aldehydes.

A specific object of this invention is to provide a process for preparing para-xylene by condensing, in separate stages, acetone, acetaldehyde and propionaldehyde and separating the desired para-xylene from any orthoxylene which may form therein.

One embodiment of this invention resides in a process for the preparation of poly-substituted benzene hydrocarbons which comprises condensing an aldehyde having the formula: RCH CHO, in which R is selected from the 2 group consisting of hydrogen and hydrocarbon radicals with an aldehyde having the formula: RCH CHO in which R is a hydrocarbon radical, further condensingthe resultant product with a ketone having the formula:

RIIg CHZ RIII in which R" is a hydrocarbon radical and R' is selected from the group consisting of hydrogen and hydrocarbon radicals, and recovering the resultant poly-substituted benzene hydrocarbons.

Another embodiment of this invention resides. in a process for the preparation of para-Xylene which comprises condensing acetaldehyde and propionaldehyde, further condensing the resultant products with acetone, and thereafter separating the resultant ortho-xylene from the para-xylene.

A specific embodiment of the invention resides in a method for preparing para-xylene by condensing acetaldehyde and propionaldehyde in the presence of an acidic condensation catalyst at a temperature in the range of from about 0 to about 400 C., further condensing the resultant products with acetone, and thereafter separating the resultant para-xylene from ortho-xylene.

A more specific embodiment of the invention is found in a process for preparing para-xylene by condensing acetaldehyde and propionaldehyde in the presence of activated alumina at a temperature in the range of from about 100 to about 400 C., further condensing the resultant products with acetone in the presence of an acidic catalyst, and thereafter separating the resultant para-xylene from ortho-xylene.

A still more specific embodiment of the invention resides in a process for preparing para-xylene which comprises condensing equimolar proportions of propionalde hyde and acetaldehyde in the presence of alumina at a temperature in the range of from about 100 to about 400 C., further condensing the resultant 2-methyl-3- hydroxybutyraldehyde and 3-hydroxyvaleraldehyde with an equimolar proportion of acetone in the presence of sulfuric acid at a temperature in the range of from about 0 to 80 C., and thereafter separating the resultant para-xylene from ortho-xylene.

Other objects and embodiments of the invention referring to alternative ketones and aldehydes will be found in the following further detailed description of the invention.

It is now proposed that polyalkyl substituted, and particularly, orthoand para-dialkyl substituted aromatic compounds be prepared by reacting or condensing equimolar quantities of ketones and aldehydes, the particular reactants used being dependent upon the length and number of the alkyl substituents on the aromatic ring. One of the aldehydic reactants which may be used in this invention are those having the general formula X-CH -CHO in which X comprises either a hydrogen radical, a halogen, nitro, sulfo, carboxy, carboxamido, hydroxy, etc. radical, or a hydrocarbon or hydrocarbon radical containing a substituent hereinbefore enumerated. The other aldehydic reactant used in the reaction has the general formula:

X Y-iJ-CHr-CHO l in which X, Y and Z are independently selected from those substituents already listed above. The remaining reactant comprises a ketonehaving the general formula:

ca l

in which T, X, Y and Z are independently chosen from the hereinabove mentioned substituents. In the process of this invention, the preferred reactants comprise acetone, acetaldehyde and propionaldehyde. Other reactants which may be used include ethyl methyl ketone, diethyl ketone, methyl propyl ketone, ethyl propyl ketone, etc., butyraldehyde, valeric aldehyde, etc., or their T, X, Y and Z substituted homologues, such as chloroacetaldehyde, nitroacetaldehyde, ,8-chloropropionaldehyde, ,BJB-dichloropropionaldehyde, B-nitropropionaldehyde, ,B-sulfopropionaldehyde, p,fi,/3-trichloropropionaldehyde, etc, a,ot'-(iiChlO- roacetone, although not necessarily with equivalent results. It is to be understood that the above mentioned compounds are only examples of the aldehydes and ketones which may be used in this process and that said process is not necessarily limited to said compounds.

The reactions of this invention may be carried out in the presence of either acidic or mildly basic condensation and dehydration catalysts, preferably solid condensation catalysts such as, for example, activated alumina, zirconia, silica, magnesia, etc., silica-alumina, silica-zirconia, silicamagnesia, alumina-Zirconia, silica-aluminamagnesia, etc. With such solid catalysts, the reaction is carried out at elevated temperatures ranging from about 100 to about 400 C. or more, and preferably at a pressure low enough that the reaction proceeds in the vapor phase. With the homogeneous catalysts, i. e. acidic or basic materials such as, for example, zinc chloride, mineral acids, such as hydrochloric or sulfuric acid, for example, amines and their mineral acid salts, sodium acetate, potassium tormate, sodium carbonate, potassium hydroxide, potassium cyanide, and the like, the reaction may be carried out at a somewhat lower temperaturefrom about C. to about 150 C., and preferably at pressures suflicient to maintain at least part of the reactants in liquid phase.

The products resulting from the condensation of equimolar proportions of acetone, acetaldehyde and propionaldehyde as described herein comprise a mixture of oand p-xylene, which, due to the relatively wide disparity in boiling points (o-xylene boiling at 144.4 C. and pxylene boiling at 138.4 C.) enables, the two xylenes to be easily separated by fractional distillation.

The reaction of this invention may be effected in any suitable manner and may comprise either a batch or continuous type operation. When a batch type operation is used, a quantity of each of the starting materials in equimolar proportions is placed in a suitable reaction vessel containing the desired catalyst. The vessel is then heated to the desired temperature and maintained thereat for a predetermined residence time. At the end of this time, the vessel and contents are cooled to room temperature and the reaction product separated by conventional means, such as fractional distillation.

When a continuous type operation is used, the starting materials are each continuously charged, in a separate stream, or two combined in one stream while the other is independently and subsequently admitted, to a reactor containing the desired catalyst and maintained at suitable operating conditions of temperature and pressure. The reactor may be an unlined vessel or coil or may contain an adsorbent material such as fire brick, dehydrated bauxite, or the like. Upon completion of the desired residence time, the products of the reaction comprising the oand p-dialkyl substituted aromatic compounds are continuously withdrawn and subjected to fractional distillation whereby the p-dialkyl substituted aromatic compound is separated from the o-dialkyl substituted aromatic compound and/or unreacted starting materials which may be present. In the preferred type of operation, as hereinafter described, two of the reactants are allowed to react to form condensation products, these are removed and by fractional distillation a fraction comprising the condensation product of one mol of each of 4 the reactants is recovered from those by-products formed from two mols of one of the reactants, and said fraction is then allowed to react with the third reactant to form the desired end-products (i. e., orthoand para-disubstituted aromatic hydrocarbons) which are then easily separated by fractionation.

This preferred continuous type of operation is used in order to minimize the interaction of two mols of any of the reactants with 1 mol of the other reactant, said reaction resulting in a yield of undesired side products or less valuable reaction products. For example, the interaction of 2 mols of acetone or 2 mols of propionaldehyde with 1 mol of acetaldehyde would result in the production of m-xylene, a particularly undesirable product in the preparation of p-xylene, due to the fact that the m-xylene and p-xylene boil within 1 C. of each other.

Yet another alternative which may be used is to add the third component of the reaction mixture down-stream of the point of introduction of the first two reactants in the same reactor, although this alternative generally gives lower yields of the desired products than the previous method in which the bimolecular intermediate condensation product is separately recovered and then subjected to further reaction.

In the interaction of acetaldehyde, propionaldehyde, and acetone to make xylenes, the reaction may be regarded as occurring in two stages-interaction of two of the components as a first stage, and condensation of the intermediate product with the third component as a second stage. If all three reactants were to be mixed and the reaction were to proceed non-seelctively, the purpose of this invention would be defeated, since equal amounts of ortho-, metaand para-xylenes would be formed and there would be, in addition, considerable amounts of open-chain by-products and condensation products containing fewer or more than eight carbon atoms. The preferred method of operation avoids these undesirable possibilities by a careful control of the order in which the reactions are allowed to proceed. This order is determined from the following considerations:

If the initial intermediate reaction is to be one between propionaldehyde and acetone, the two intermediates will be (A) on condensation with acetaldehyde, ring closure, and dehydration yields para-xylene; (B) yields orthoxylene. But (A) and (B) are contaminated with bimolecular condensation products of two mols of acetone (diacetone alcohol) and of two mols of propionaldehyde, each of which, with acetaldehyde, yields metaxylene (which is an undesirable product), and each of which, like (A) and (B) contains six carbon atoms. From this mixture of six carbon bimolecular intermediate products it is difiicult to separate the desirable compo nents from the undesirable, so that the reaction of propionaldehyde with acetone is not a preferred initial step.

A second possible initial step is the reaction of acetaldehyde with acetone. In this case, two five carbon intermediates are possible:

(CHa)zC-CH2CHO (D) Both of these five carbon intermediates should be easily separable from aldol and diacetone alcohol formed as a result of the concurrent condensation of two mols of acetaldehyde or two mols of acetone, respectively. But of the two intercondensation products (C) and (D), it is found that (C) is formed preferentially; and (C), on interaction with propionaldehyde, yields ortho-xylene or open-chain products, while (D) yields paraxylene. The yields of para-xylene by this route are therefore poorer than desirable (although good yields of orthoxylene maybe obtained) and it is not the preferred method for preparing para-xylene.

The third (and preferred) initial reaction is that between acetaldehyde and propionaldehyde. Here again, two intercondensation products are possible, and these, since they contain five carbon atoms, are separable without difliculty from the four carbon or six carbon products formed by condensation of two mols of either of the reactants. The intercondensation products are:

and

Example I 88 g. of acetaldehyde and 116 g. of propionaldehyde are placed in an autoclave, and 5 grams of powdered anhydrous potassium carbonate added. The autoclave is sealed and the reaction is allowed to proceed for 24 hours at about 50 C. At the end of this time, the autoclinic and contents thereof are cooled and thereaction products removed, washed, and distilled. A fraction comprising the material boiling at 87-97 C. (20 mm.)

is recovered (weight, 105 g.). This is mixed with 60 g.

acetone, and to the mixture is added 250 g. of cold 63% sulfuric acid. The mixture is maintained at 25 C. and stirred for twenty hours, after which it is distilled, the water condensed from the distillation overhead being continuously returned to the still to prevent the sulfuric acid from becoming too concentrated. The organic condensate is distilled, yielding a fraction boiling at 135-" 145 C. which weighs 48 g. and contains approximately 70% para-xylene and 30% ortho-xylene, which is redistilled to yield a fraction of pure para-xylene.

Example II 88 g. of acetaldehyde and 116 g. of propionaldehyde are placed in an autoclave along with 5 g. of activated alumina. The autoclave is sealed and heated to a temperature of approximately 125 C., at which temperature the reaction is allowed to proceed for 24 hours. At the end of this time the autoclave and contents thereof are cooled, and the reaction products, comprising a mixture of 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde are removed, washed and distilled.

The fraction boiling between 87 and 97 C. (20 mm.) is recovered and mixed with 60 g. of acetone. Cold sulfuric acid of the type set forth in Example I is added to the mixture which is thereafter maintained at a temperature of approximately 25 C. for 20 hours. At the a 6 end of this time the mixture is distilled in a manner similar to that hereinbefore set forth in Example I to recover the para-xylene.

I claim as my invention:

1. A process for the preparation of para-xylene which comprises condensing equimolar proportions of propionaldehyde and acetaldehyde in the presence of an acidic condensation catalyst selected from the group consisting of alumina, zirconia, silica, magnesia, zinc chloride, hydrochloric acid and sulfuric acid at a temperature in the range of from about 0 to about 400 C., separating the resultant 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from the reaction mixture and further condensing the same with an equimolar proportion of acetone in the presence of an acidic catalyst selected from the group aforesaid at a temperature in the range of from about 0 to 80 C., and separating the resultant para-xylene from ortho-xylene.

2. A process for the preparation of para-xylene which comprises condensing equimolar proportions of acetaldehyde and propionaldehyde in the presence of a silicacontaining catalyst at a temperature in the range of from about 100 to about 400 C., thereafter separating the resultant 2-methy1-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from the reaction mixture and further condensing the same with an equimolar proportion of acetone in the presence of sulfuric acid at a temperature in the range of from about 0 to 80 C., and separating the resultant para-xylene from orthoxylene.

3. A process for the preparation of para-xylene which comprises condensing equimolar proportions of propionaldehyde and acetaldehyde in the presence of a zirconia catalyst at a temperature in the range of from about 100 to about 400 C., separating the resultant 2-methyl-3- hydroxybutyraldehyde and 3-hydroxyvalera1dehyde from the reaction mixture and further condensing the same with an equimolar proportion of acetone in the presence of sulfuric acid at a temperature in the range of from about 0 to 80 C., and thereafter separating the resultant para-xylene from ortho-xylene.

4. A process for the preparation of para-xylene which comprises condensing equimolar proportions of propionaldehyde and acetaldehyde in the presence of alumina at a temperature in the range of from about 100 toabout 400 C., separating the resultant 2-methyl-3-hydroxybutyraldehyde and 3-hydroxyvaleraldehyde from the reaction mixture and further condensing the same with an equimolar proportion of acetone in the presence of sulfuric acid at a temperature in the range of from about 0 to 80 C., and thereafter separating the resultant paraxylene from ortho-xylene.

5. A process for the preparation of para-xylene which comprises condensing equimolar proportions of acetaldehyde and propionaldehyde in the presence of zinc chloride at a temperature in the range of from about 0 to about 150 C., separating the resultant 2-methyl-3-hy- References Cited in the file of this patent Adkins et al.: Iour. Am. Chem. Soc., vol. 53, pages 2714-20 (1931).

Whitmore: D. Van Nostrand Co., 250 4th Ave., New York, N. Y.

Berkman et al.: Catalysis (1940), page 693. Reinhold Publishing Corp., 330 W. 42nd St., New York, N. Y.

Organic Chemistry (1937), page 236. 

1. A PROCESS FOR THE PREPARATION OF PARA-XYLENE WHICH COMPRISES CONDENSING EQUIMOLAR PROPORTIONS OF PROPIONALDEHYDE AND ACETALDEHYDE IN THE PRESENCE OF AN ACIDIC CONDENSATION CATALYST SELECTED FROM THE GROUP CONSISTING OF ALUMINA, ZIRCONIA, SILICA, MAGNESIA, ZINC CHLORIDE, HYDROCHLORIC ACID AND SULFURIC ACID AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0* TO ABOUT 400*C., SEPARATING THE RESULTANT 2-METHYL-3-HYDROXYBUTYRALDEHYDE AND 3-HYDROXYVALERALDEHYDE FROM THE REACTION MIXTURE AND FURTHER CONDENSING THE SAME WITH AN EQUIMOLAR PROPORTION OF ACETONE IN THE PRESENCE OF AN ACIDIC CATALYST SELECTED FROM THE GROUP AFORESAID AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 0* TO 80*C., AND SEPARATING THE RESULTANT PARA-XYLENE FROM ORTHO-XYLENE. 